Semicoffer or ship caisson



July 18, 1939. H. GERDES SEMICOFFER OR SHIP CAISSON IN E/Var Filed Nov. 10, 1936 A l I Patented July 18, 1939 UNITED STATES PATENT OFFICE.

Application November 10, 1936, Serial No. 110,167 In Germany November 12, 1935 6 Claims.

It has been observed that in the case'of sheet pilings very strong corrosion often takes place under water as the pilingsare not-sufficiently protected against corrosion; Experience has shown that the corrosion is strongest at a certain distance below the normal water level. Ina North Sea port, for example it has been noticed that the corrosionzone was greatest in iron structures within the section of the harbor partitioned off byseal looks at about l-rneter below the normal, relatively constant water level, and that inthe case-of iron structures outside the sea locks, where the waterlevel varies daily on an average about 3 /2-meters owing-to the tide, the greatest corrosion occurred at about l meter below the mean low water level.

Hitherto it has not been-possible to protect sheet pilings under-water against corrosion after their erection. Furthermore no serious endeavourshavebeen made forthe preservation below Water because the general opinion was that a considerable weakening. through corrosion-need notabe feared. However, according tothe latest observations above set .forththis isnot the case and experts are gradually becomingconvinced that in many instances something radical must be undertaken to preserve thesheet pilings below water. Thisis the more necessary because the points under water which.aremoststronglyattackedby corrosion coincide with thoseportions of the sheet piling subjected to the greatest bending moments. Precisely. these .points are least suitable to stand a reduction. in cross-section and the resultantreduction in strength of the iron remaining. standing.

It is known that the coat of. protective-painting applied on the water sidebefore the ramming does not remain effective for along period, more particularly in the case of aggressive waters (sea water) and, whenliving. creatures (balanoids, Baldnus balanoides L) .are present, which destroy the. coating, thus enabling the water. to come into contact with the iron. As long as it is not possible to provide an efiective protection against corrosionof the portions of the sheet piling below Water, the Walls of the iron sheet piling, must be made thicker than wouldotherwisebe necessary,.so as to take into consideration this weakening effect due to. corrosion. In the case of important structures substitute structures may becomeprematurely necessary, because nothing is known concerning the extent of corrosion. Finally, the, question of. the protection against destruction due to corrosion must have an .infiuence on the selection of thematerial. in .planning.

The new method'for preserving-iron sheet pilings andother structuralparts below water consistsin-draining off the water from the surfaces of the sheet pilings in question by means of a coffer or caisson. Experience has shown, that a sufficiently long time is required for thoroughly drying the sheet pilings, if necessary with hotair, removing the rust (with sand blast) and painting them, to obtain efiective preservation. The cofier or caisson is provided with floats to enable it to be easily brought into the position for-use at aminimum expense; an arrangement is also provided on the cofier forreceiving ballast (preferably ballast tanks). When the coffer is in horizontal floating position all packing surfaces can be-easily fitted and repaired. At the place of use the coffer is brought intoits vertical floating position and sunk tothe desired depth by flooding a ballast tank. The depth of immersion can be easily regulated by operating the fiooding valves andthe shut-off devices on airpipes leading to the tanks.- The coffer, when in vertical floating position, is. brought tightly against the piling and emptied by bilge pumps preferably mounted on the coffer. The coffer is pressed-against the piling by the external water pressure, so that a tight closure is produced. It is, however, necessary. to counteract the upward pressure acting on the bottom of the coffer. This isefiected by further flooding all the existing ballast tanks tothe required extent. It is particular- 1y important that the coffer be sufficiently loaded by ballast water as the wall friction between the smooth piling. and the packing materials on the cofier. (rubber, hemp, mats or thelike) isslight. The buoyancy iscounteracted by the constructional weight of the coffer and'of the ballastwater admitted. If necessary, the ballast tanks must extend slightly above the water level to allow additional quantities of ballast water to be filled therein by a water feed pipe or by a pump- Further details are shown in the accompanying drawing showing the coffer illustrated by way of example, in which Fig. 1 is a vertical section of the cofier fitted on asheet piling.

Fig. 2 is a horizontal sectional View taken on the line 22 of Fig. 1.

Fig. 3 is a front elevation of the device shown in Fig. 1.

Fig. 4 is a horizontal sectional view similar to Fig. 2 but showing a modified form of construction of the coifer.

The coffer a. has on its outer side at its ,upper end peripheral float andballast tanks 1). .Fur-.

thermore, floating boxes I), subdivided by horizontal bulkheads b extend along the entire height of the longitudinal sides of the coffer and serve at the same time as capsizing tanks.

Fig. 3 shows for example a subdivision of each tank into two compartments b by a horizontal bulkhead U. The open side has a packing frame 0 removably fixed on the coffer a and bearing against the surface of the sheet piling d. When the coifer has been brought in. the required position against the sheet piling and suitably anchored, the space 0 provided between the structurethe outer surface of the sheet piling dand the coffer a is pumped dry, the ballast tanks being at the same time filled, so that the coffer bears tightly against the structure by means of the packing frame 0 and is secured against emersion. The necessary work--for example painting of the exposed portion of the sheet piling is carried out through the packing frame 0 within the protection of the space thus formed.

To prevent the stock of coffers necessary for accelerating the work from becoming too large in the case of high sheet piling the invention provides means shown in Fig. 4 for externally shutting off the loaded packing frame on the spot by a plate 9 to enable the coffer to be removed and the surface to dry or harden. In this manner the painted surface will be protected by the space formed between the packing frame and the plate.

A packing frame 0 of this construction with inserted removable plate g is shown in horizontal :section in Fig. 4.

The packing frame (1 differs from the frame 0 in Fig. 1, in that it is provided with a continuous channel 1 designed to accommodate the plate 9- This channel may be lined with rubber or other suitable .material (not shown) to provide a watertight channel for the plate 9.

The packing frame 0 as well as the frame 6, are provided extensions 0 which are adapted to the undulating shape of the sheet piling. These extensions 0 may be secured to the frames by bolts mv as shown in Fig. l. In this figure, the bolts m extend through the extensions 0 frame 0 and channel member 2. It will also be observed in this figure of the drawing that these bolts do not extend through the plate 9 but are arranged beneath said plate.

In this modification of the invention, the coffer a is detachably connected to the frame 03 by bolts it. These bolts may be loosened from the interior of the coffer after the painting is completed and before the plate g is inserted in the channel. The complete removal of the bolts it may be accomplished from the exterior of the coifer, after the plate 9' has been inserted in the channel I. By removing the bolts 71. the coffer is disconnected from the frame and may be transferred to another location fora further painting operation.

After the coffer a has been removed from the frame 0 the plate 9 in the channel 1 will maintain the frame pressed against the piling due to the water pressure exerted against said plate. However, since the plate g must withstand a considerable water pressure, I preferably provide said plate with supports 2' which bear against the ribs 7c of the piling. To prevent the supports 2' on the plate from adhering too tightly against the sheet piling, it is advisable to provide strips 1 of wool felt board, sheet metal or the like between the supports 2 and the ribs 7c of the piling.

With this arrangement it will be seen that the freshlypainted surface of the piling may be protected by the space formed between the packing frame 0 and the plate g until the paint has dried or hardened. When the surface has dried or hardened, the space between the plate and the piling is filled with water so that the plate can easily be pulled out of the water.

I claim:

1. A cofier of the class described for carrying out work on submerged structures, comprising, a bottom wall, spaced vertical walls secured to said bottom wall, partitions connecting said walls to form a plurality of fluid-tight ballast chambers, said vertical walls being spaced from the innermost edge of the bottom wall to form a vertical working space, and a packing member secured to said walls, said packing member forming a frame comprising a lower member conforming to the contour of the submerged structure, and a pair of spaced vertical members secured to said lower member, and a removable plate slidably mounted on said frame and spaced from the submerged structure.

2. A coffer of the class described for carrying out work on submerged structures comprising, a bottom wall, spaced vertical walls secured to said bottom wall, partitions connecting said walls to form a plurality of fluid tight ballast chambers, said vertical walls being spaced from the innermost edge of the bottom wall to form a vertical working space, and a packing member secured to said Walls, said packing member forming a frame comprising a lower member conforming to the contour of the submerged structure, a pair of spaced vertical members secured to said lower member, said last mentioned members having cutaway portions defining a channel, and a removable plate slidably mounted in said channel and forming with said vertical members and said lower member a fluid tight joint, said plate being spaced from the submerged structure.

3. A coffer of the class described for carrying out work on submerged structures comprising, a bottom wall, spaced vertical walls secured to said bottom wall, partitions connecting said walls to form a plurality of fluid tight ballast chambers, said vertical walls being spaced from the innermost edge of the bottom wall to form a vertical working space, and a packing member secured to said walls, said packing member forming a frame comprising a lower member conforming to the contour of the submerged structure and a pair of spaced vertical members secured to said lower member, a removable plate slidably mounted on said frame, and spaced from the submerged structure, and supporting members secured to said plate and interposed between said submerged structure and said plate.

4. A coffer of the class described for carrying out work on submerged structures comprising, a bottom wall, spaced vertical walls secured to said bottom wall, partitions connecting said walls to form a plurality of fluid tight ballast chambers, said vertical walls being spaced from the innermost edge of the bottom wall to form a vertical working space, and a packing member secured to said walls, said packing member forming a frame comprising a lower member conforming to the contour of the submerged structure and a pair of spaced vertical members secured to said lower member, a channel member secured to said frame and spaced from the submerged structure, a removable plate slidably mounted in said channel member, supporting members secured to said plate and adapted to abut against the submerged structure, and yielding means lining the abutting surface of said supports.

6. A cofier of the class described for carrying out work on submerged structures having a nonplanar surface, comprising a bottom wall, spaced vertical walls secured to said bottom wall, said vertical walls being spaced from the innermost edge of the bottom Wall to form a vertical Working space, a packing member shaped to fit against said non-planar surface at the bottom wall and interposed between said Walls and the submerged structure, and fastening means for disconnecting 10 said Walls from said packing member.

HANS GERDES. 

